1. Field of the Invention
The present invention is directed to a method and an apparatus for data acquisition, particularly for the acquisition of measured data in real time.
2. Description of the Prior Art
Large datasets arise in certain measuring procedures in devices that acquire measured data. Such devices include, for example, image-generating medical devices such as a tomography apparatus, an angiography apparatus. These devices offer the data with a predetermined, usually extremely high, data rate and the data must be forwarded to a processing computer in real time or nearly in real time. If excessively great delays occur in the acceptance of the data by the processing computer, then data are lost because the ongoing measuring procedure cannot be arrested. The measurement must then be repeated.
German OS 42 31 580 discloses a method and an apparatus wherein a continuous data flow generated by a data source is written into a data buffer memory. A driver module, on an operating system level of a data processing system, controls a DMA transfer of data from the data buffer memory into an input/output memory. Each DMA transfer fills an elementary buffer of the input/output memory. Data acquisition rates of more than 600 kBytes per second are possible with this method.
A problem associated with the method disclosed in German OS 42 31 580 is that the DMA transfer has a permanently prescribed length and the data that are read in can only be further-processed after the termination of the DMA transfer. In some measuring procedures, however, it is desirable to immediately interpret shorter data blocks. For example, artefacts that are caused by the movement of the rib cage during respiration can occur in nuclear magnetic tomographic measurements of the heart of a patient. In order to find a point in time of optimum rest of the rib cage for the actual measurement, a number of short measurements perpendicular to the plane of the diaphragm are implemented first. Relatively few data, which must be immediately interpreted, arise in these short measurements. The actual measurement, wherein large datasets arise and must be transmitted, is initiated as soon as a predetermined position of the rib cage is recognized on the basis of the interpretation of the short measurements.